'\" te
.\" Copyright 1989 AT&T.
.\" Copyright (c) 2006, Sun Microsystems, Inc.  All Rights Reserved.
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH PRIOCNTL 2 "Feb 17, 2023"
.SH NAME
priocntl \- process scheduler control
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <sys/priocntl.h>
#include <sys/rtpriocntl.h>
#include <sys/tspriocntl.h>
#include <sys/iapriocntl.h>
#include <sys/fsspriocntl.h>
#include <sys/fxpriocntl.h>

\fBlong\fR \fBpriocntl\fR(\fBidtype_t\fR \fIidtype\fR, \fBid_t\fR \fIid\fR, \fBint\fR \fIcmd\fR, \fB/*\fR \fIarg\fR */ ...);
.fi

.SH DESCRIPTION
The \fBpriocntl()\fR function provides for control over the scheduling of an
active light weight process (LWP).
.sp
.LP
LWPs fall into distinct classes with a separate scheduling policy applied to
each class. The classes currently supported are the realtime class, the
time-sharing class, the fair-share class, and the fixed-priority class. The
characteristics of these classes are described under the corresponding headings
below.
.sp
.LP
The class attribute of an LWP is inherited across the \fBfork\fR(2) function
and the \fBexec\fR(2) family of functions. The \fBpriocntl()\fR function can be
used to dynamically change the class and other scheduling parameters associated
with a running LWP or set of LWPs given the appropriate permissions as
explained below.
.sp
.LP
In the default configuration, a runnable realtime LWP runs before any other
LWP. Therefore, inappropriate use of realtime LWP can have a dramatic negative
impact on system performance.
.sp
.LP
The \fBpriocntl()\fR function provides an interface for specifying a process,
set of processes, or an LWP to which the function applies. The
\fBpriocntlset\fR(2) function provides the same functions as \fBpriocntl()\fR,
but allows a more general interface for specifying the set of LWPs to which the
function is to apply.
.sp
.LP
For \fBpriocntl()\fR, the \fIidtype\fR and \fIid\fR arguments are used together
to specify the set of LWPs. The interpretation of \fIid\fR depends on the value
of \fIidtype\fR. The possible values for \fIidtype\fR and corresponding
interpretations of \fIid\fR are as follows:
.sp
.ne 2
.na
\fB\fBP_ALL\fR\fR
.ad
.RS 12n
The \fBpriocntl()\fR function applies to all existing LWPs. The value of
\fIid\fR is ignored. The permission restrictions described below still apply.
.RE

.sp
.ne 2
.na
\fB\fBP_CID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a class ID (returned by the \fBpriocntl()\fR
\fBPC_GETCID\fR command as explained below). The \fBpriocntl()\fR function
applies to all LWPs in the specified class.
.RE

.sp
.ne 2
.na
\fB\fBP_GID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a group ID. The \fBpriocntl()\fR function applies to
all LWPs with this effective group ID.
.RE

.sp
.ne 2
.na
\fB\fBP_LWPID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is an LWP ID. The \fIpriocntl\fR function applies to the
LWP with the specified ID within the calling process.
.RE

.sp
.ne 2
.na
\fB\fBP_PGID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a process group ID. The \fBpriocntl()\fR function
applies to all LWPs currently associated with processes in the specified
process group.
.RE

.sp
.ne 2
.na
\fB\fBP_PID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a process ID specifying a single process. The
\fBpriocntl()\fR function applies to all LWPs currently associated with the
specified process.
.RE

.sp
.ne 2
.na
\fB\fBP_PPID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a parent process ID. The \fBpriocntl()\fR function
applies to all LWPs currently associated with processes with the specified
parent process ID.
.RE

.sp
.ne 2
.na
\fB\fBP_PROJID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a project ID. The \fBpriocntl()\fR function applies to
all LWPs with this project ID.
.RE

.sp
.ne 2
.na
\fB\fBP_SID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a session ID. The \fBpriocntl()\fR function applies to
all LWPs currently associated with processes in the specified session.
.RE

.sp
.ne 2
.na
\fB\fBP_TASKID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a task ID. The \fBpriocntl()\fR function applies to
all LWPs currently associated with processes in the specified task.
.RE

.sp
.ne 2
.na
\fB\fBP_UID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a user ID. The \fBpriocntl()\fR function applies to
all LWPs with this effective user ID.
.RE

.sp
.ne 2
.na
\fB\fBP_ZONEID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a zone ID. The \fBpriocntl()\fR function applies to
all LWPs with this zone ID.
.RE

.sp
.ne 2
.na
\fB\fBP_CTID\fR\fR
.ad
.RS 12n
The \fIid\fR argument is a process contract ID. The \fBpriocntl()\fR function
applies to all LWPs with this process contract ID.
.RE

.sp
.LP
An \fIid\fR value of \fBP_MYID\fR can be used in conjunction with the
\fIidtype\fR value to specify the LWP ID, parent process ID, process group ID,
session ID, task ID, class ID, user ID, group ID, project ID, zone ID, or
process contract ID of the calling LWP.
.sp
.LP
To change the scheduling parameters of an LWP (using the \fBPC_SETPARMS\fR or
\fBPC_SETXPARMS\fR command as explained below), the real or effective user ID
of the LWP calling \fBpriocntl()\fR must match the real or the calling LWP must
have sufficient privileges. These are the minimum permission requirements
enforced for all classes. An individual class might impose additional
permissions requirements when setting LWPs to that class and/or when setting
class-specific scheduling parameters.
.sp
.LP
A special \fBSYS\fR scheduling class exists for the purpose of scheduling the
execution of certain special system processes (such as the swapper process). It
is not possible to change the class of any LWP to \fBSYS\fR. In addition, any
processes in the \fBSYS\fR class that are included in a specified set of
processes are disregarded by \fBpriocntl()\fR. For example, an \fIidtype\fR of
\fBP_UID\fR and an \fIid\fR value of 0 would specify all processes with a user
ID of 0 except processes in the \fBSYS\fR class and (if changing the parameters
using \fBPC_SETPARMS\fR or \fBPC_SETXPARMS\fR) the \fBinit\fR(8) process.
.sp
.LP
The \fBinit\fR process is a special case. For a \fBpriocntl()\fR call to change
the class or other scheduling parameters of the \fIinit\fR process (process ID
1), it must be the only process specified by \fIidtype\fR and \fIid\fR. The
\fBinit\fR process can be assigned to any class configured on the system, but
the time-sharing class is almost always the appropriate choice. (Other choices
might be highly undesirable. See the \fISystem Administration Guide: Basic
Administration\fR for more information.)
.sp
.LP
The data type and value of \fIarg\fR are specific to the type of command
specified by \fIcmd\fR.
.sp
.LP
A \fBpcinfo_t\fR structure with the following members, defined in
\fB<sys/priocntl.h>\fR, is used by the \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR
commands.
.sp
.in +2
.nf
id_t   pc_cid;                   /* Class id */
char   pc_clname[PC_CLNMSZ];     /* Class name */
int    pc_clinfo[PC_CLINFOSZ];   /* Class information */
.fi
.in -2

.sp
.LP
The \fIpc_cid\fR member is a class ID returned by the \fBpriocntl()\fR
\fBPC_GETCID\fR command.
.sp
.LP
The \fIpc_clname\fR member is a buffer of size \fBPC_CLNMSZ\fR, defined in
\fB<sys/priocntl.h>\fR, used to hold the class name: \fBRT\fR for realtime,
\fBTS\fR for time-sharing, \fBIA\fR for interactive, \fBFSS\fR for fair-share,
or \fBFX\fR for fixed-priority. Each string is null-terminated.
.sp
.LP
The \fIpc_clinfo\fR member is a buffer of size \fBPC_CLINFOSZ\fR, defined in
\fB<sys/priocntl.h>\fR, used to return data describing the attributes of a
specific class. The format of this data is class-specific and is described
under the appropriate heading (\fBREALTIME CLASS\fR, \fBTIME-SHARING CLASS\fR,
\fBINTERACTIVE CLASS\fR, \fBFAIR-SHARE CLASS\fR, or \fBFIXED-PRIORITY CLASS\fR)
below.
.sp
.LP
A \fBpcparms_t\fR structure with the following members, defined in
\fB<sys/priocntl.h>\fR, is used by the \fBPC_SETPARMS\fR and \fBPC_GETPARMS\fR
commands.
.sp
.in +2
.nf
id_t  pc_cid;                   /* LWP class */
int   pc_clparms[PC_CLPARMSZ];  /* Class-specific params */
.fi
.in -2

.sp
.LP
The \fIpc_cid\fR member is a class ID returned by the \fBpriocntl()\fR
\fBPC_GETCID\fR command. The special class ID \fBPC_CLNULL\fR can also be
assigned to \fIpc_cid\fR when using the \fBPC_GETPARMS\fR command as explained
below.
.sp
.LP
The \fIpc_clparms\fR buffer holds class-specific scheduling parameters. The
format of this parameter data for a particular class is described under the
appropriate heading below. \fBPC_CLPARMSZ\fR is the length of the
\fIpc_clparms\fR buffer and is defined in \fB<sys/priocntl.h>\fR.
.sp
.LP
The \fBPC_SETXPARMS\fR and \fBPC_GETXPARMS\fR commands exploit the
\fBvarargs\fR declaration of \fBpriocntl()\fR. The argument following the
command code is a class name: \fBRT\fR for realtime, \fBTS\fR for time-sharing,
\fBIA\fR for interactive, \fBFSS\fR for fair-share, or \fBFX\fR for
fixed-priority. The parameters after the class name build a chain of (key,
value) pairs, where the key determines the meaning of the value within the
pair. When using \fBPC_GETXPARMS\fR, the value associated with the key is
always a pointer to a scheduling parameter. In contrast, when using
\fBPC_SETXPARMS\fR the scheduling parameter is given as a direct value.  A key
value of \fB0\fR terminates the sequence and all further keys or values are
ignored.
.sp
.LP
The \fBPC_SETXPARMS\fR and \fBPC_GETXPARMS\fR commands are more flexible than
\fBPC_SETPARMS\fR and \fBPC_GETPARMS\fR and should replace \fBPC_SETPARMS\fR
and \fBPC_GETPARMS\fR on a long-term basis.
.SH COMMANDS
Available \fBpriocntl()\fR commands are:
.sp
.ne 2
.na
\fB\fBPC_ADMIN\fR\fR
.ad
.RS 16n
This command provides functionality needed for the implementation of the
\fBdispadmin\fR(8) utility. It is not intended for general use by other
applications.
.RE

.sp
.ne 2
.na
\fB\fBPC_DONICE\fR\fR
.ad
.RS 16n
Set or get nice value of the specified LWP(s) associated with the specified
process(es). When this command is used with the \fIidtype\fR of \fBP_LWPID\fR,
it sets the nice value of the LWP. The \fIarg\fR argument points to a structure
of type \fBpcnice_t\fR. The \fIpc_val\fR member specifies the nice value and
the \fIpc_op\fR specifies the type of the operation.
.sp
When \fIpc_op\fR is set to \fBPC_GETNICE\fR, \fBpriocntl()\fR sets the
\fIpc_val\fR to the highest priority (lowest numerical value) pertaining to any
of the specified LWPs.
.sp
When \fIpc_op\fR is set to \fBPC_SETNICE\fR, \fBpriocntl()\fR sets the nice
value of all LWPs in the specified set to the value specified in \fIpc_val\fR
member of \fBpcnice_t\fR structure.
.sp
The \fBpriocntl()\fR function returns \fB\(mi1\fR with \fBerrno\fR set to
\fBEPERM\fR if the calling LWP doesn't have appropriate permissions to set or
get nice values for one or more of the target LWPs. If \fBpriocntl()\fR
encounters an error other than permissions, it does not continue through the
set of target LWPs but returns the error immediately.
.RE

.sp
.ne 2
.na
\fB\fBPC_GETCID\fR\fR
.ad
.RS 16n
Get class ID and class attributes for a specific class given the class name.
The \fIidtype\fR and \fIid\fR arguments are ignored. If \fIarg\fR is non-null,
it points to a structure of type \fBpcinfo_t\fR. The \fIpc_clname\fR buffer
contains the name of the class whose attributes you are getting.
.sp
On success, the class ID is returned in \fBpc_cid\fR, the class attributes are
returned in the \fIpc_clinfo\fR buffer, and the \fBpriocntl()\fR call returns
the total number of classes configured in the system (including the \fBsys\fR
class). If the class specified by \fIpc_clname\fR is invalid or is not
currently configured, the \fBpriocntl()\fR call returns \fB\(mi1\fR with
\fBerrno\fR set to \fBEINVAL\fR. The format of the attribute data returned for
a given class is defined in the \fB<sys/rtpriocntl.h>\fR,
\fB<sys/tspriocntl.h>\fR, \fB<sys/iapriocntl.h>\fR, \fB<sys/fsspriocntl.h>\fR,
or \fB<sys/fxpriocntl.h>\fR header and described under the appropriate heading
below.
.sp
If \fIarg\fR is a null pointer, no attribute data is returned but the
\fBpriocntl()\fR call still returns the number of configured classes.
.RE

.sp
.ne 2
.na
\fB\fBPC_GETCLINFO\fR\fR
.ad
.RS 16n
Get class name and class attributes for a specific class given class ID. The
\fIidtype\fR and \fIid\fR arguments are ignored. If \fIarg\fR is non-null, it
points to a structure of type \fBpcinfo_t\fR. The \fIpc_cid\fR member is the
class ID of the class whose attributes you are getting.
.sp
On success, the class name is returned in the \fIpc_clname\fR buffer, the class
attributes are returned in the \fIpc_clinfo\fR buffer, and the \fBpriocntl()\fR
call returns the total number of classes configured in the system (including
the \fBsys\fR class). The format of the attribute data returned for a given
class is defined in the \fB<sys/rtpriocntl.h>\fR, \fB<sys/tspriocntl.h>\fR,
\fB<sys/iapriocntl.h>\fR, \fB<sys/fsspriocntl.h>\fR, or
\fB<sys/fxpriocntl.h>\fR header and described under the appropriate heading
below.
.sp
If \fIarg\fR is a null pointer, no attribute data is returned but the
\fBpriocntl()\fR call still returns the number of configured classes.
.RE

.sp
.ne 2
.na
\fB\fBPC_GETPARMS\fR\fR
.ad
.RS 16n
Get the class and/or class-specific scheduling parameters of an LWP. The
\fIarg\fR member points to a structure of type \fBpcparms_t\fR.
.sp
If \fIpc_cid\fR specifies a configured class and a single LWP belonging to that
class is specified by the \fIidtype\fR and \fIid\fR values or the
\fBprocset\fR structure, then the scheduling parameters of that LWP are
returned in the \fIpc_clparms\fR buffer. If the LWP specified does not exist or
does not belong to the specified class, the \fBpriocntl()\fR call returns
\fB\(mi1\fR with \fBerrno\fR set to \fBESRCH\fR.
.sp
If \fIpc_cid\fR specifies a configured class and a set of LWPs is specified,
the scheduling parameters of one of the specified LWP belonging to the
specified class are returned in the \fIpc_clparms\fR buffer and the
\fBpriocntl()\fR call returns the process ID of the selected LWP. The criteria
for selecting an LWP to return in this case is class-dependent. If none of the
specified LWPs exist or none of them belong to the specified class, the
\fBpriocntl()\fR call returns \fB\(mi1\fR with \fBerrno\fR set to \fBESRCH\fR.
.sp
If \fIpc_cid\fR is \fBPC_CLNULL\fR and a single LWP is specified, the class of
the specified LWP is returned in \fIpc_cid\fR and its scheduling parameters are
returned in the \fIpc_clparms\fR buffer.
.RE

.sp
.ne 2
.na
\fB\fBPC_GETXPARMS\fR\fR
.ad
.RS 16n
Get the class or class-specific scheduling parameters of an LWP. The class name
(first argument after \fBPC_GETXPARMS\fR) specifies the class and the (key,
value) pair sequence contains a pointer to the class-specific parameters. The
keys and the types of the class-specific parameter data are described below
and can also be found in the class-specific headers \fB<sys/rtpriocntl.h>\fR,
\fB<sys/tspriocntl.h>\fR, \fB<sys/iapriocntl.h>\fR, \fB<sys/fsspriocntl.h>\fR,
and \fB<sys/fxpriocntl.h>\fR. If the specified class is a configured class and
a single LWP belonging to that class is specified by the \fIidtype\fR and
\fIid\fR values or the \fBprocset\fR structure, then the scheduling parameters
of that LWP are returned in the given (key, value) pair buffers. If the LWP
specified does not exist or does not belong to the specified class,
\fBpriocntl()\fR returns \fB\(mi1\fR and \fBerrno\fR is set to \fBESRCH\fR.
.sp
If the class name specifies a configured class and a set of LWPs is given, the
scheduling parameters of one of the specified LWPs belonging to the specified
class are returned and the \fBpriocntl()\fR call returns the process ID of the
selected LWP. The criteria for selecting an LWP to return in this case is
class-dependent. If none of the specified LWPs exist or none of them belong to
the specified class, \fBpriocntl()\fR returns \fB\(mi1\fR and \fBerrno\fR is
set to \fBESRCH\fR.
.sp
If the class name is a null pointer, a single process or LWP is specified, and
a (key, value) pair for a class name request is given, \fBpriocntl()\fR fills
the buffer pointed to by value with the class name of the specified process or
LWP. The key for the class name request is \fBPC_KY_CLNAME\fR and the class
name buffer should be declared as:
.sp
.in +2
.nf
char   pc_clname[PC_CLNMSZ];     /* Class name */
.fi
.in -2

.RE

.sp
.ne 2
.na
\fB\fBPC_SETPARMS\fR\fR
.ad
.RS 16n
Set the class and class-specific scheduling parameters of the specified LWP(s)
associated with the specified process(es). When this command is used with the
\fIidtype\fR of P_LWPID, it will set the class and class-specific scheduling
parameters of the LWP.  The \fIarg\fR argument points to a structure of type
\fBpcparms_t\fR. The \fIpc_cid\fR member specifies the class you are setting
and the \fIpc_clparms\fR buffer contains the class-specific parameters you are
setting. The format of the class-specific parameter data is defined in the
\fB<sys/rtpriocntl.h>\fR, \fB<sys/tspriocntl.h>\fR, \fB<sys/iapriocntl.h>\fR,
\fB<sys/fsspriocntl.h>\fR, or \fB<sys/fxpriocntl.h>\fR header and described
under the appropriate class heading below.
.sp
When setting parameters for a set of LWPs, \fBpriocntl()\fR acts on the LWPs in
the set in an implementation-specific order. If \fBpriocntl()\fR encounters an
error for one or more of the target processes, it might or might not continue
through the set of LWPs, depending on the nature of the error. If the error is
related to permissions (\fBEPERM\fR), \fBpriocntl()\fR continues through the
LWP set, resetting the parameters for all target LWPs for which the calling LWP
has appropriate permissions.  The \fBpriocntl()\fR function then returns
\fB\(mi1\fR with \fBerrno\fR set to \fBEPERM\fR to indicate that the operation
failed for one or more of the target LWPs. If \fBpriocntl()\fR encounters an
error other than permissions, it does not continue through the set of target
LWPs but returns the error immediately.
.RE

.sp
.ne 2
.na
\fB\fBPC_SETXPARMS\fR\fR
.ad
.RS 16n
Set the class and class-specific scheduling parameters of the specified LWP(s)
associated with the specified process(es). When this command is used with
\fBP_LWPID\fR as \fIidtype\fR, it will set the class and class-specific
scheduling parameters of the LWP. The class name (first argument after
\fBPC_SETXPARMS\fR) specifies the class to be changed and the following (key,
value) pair sequence contains the class-specific parameters to be changed. Only
those (key,value) pairs whose scheduling behavior is to change must be
specified. The keys and the types of the class-specific parameter data are
described below and can also be found in the class-specific header files
\fB<sys/rtpriocntl.h>\fR, \fB<sys/tspriocntl.h>\fR, \fB<sys/iapriocntl.h>\fR,
\fB<sys/fsspriocntl.h>\fR, and \fB<sys/fxpriocntl.h>\fR.
.sp
When setting parameters for a set of LWPs, \fBpriocntl()\fR acts on the LWPs in
the set in an implementation-specific order. If \fBpriocntl()\fR encounters an
error for one or more of the target processes, it might or might not continue
through the set of LWPs, depending on the nature of the error. If the error is
related to permissions (\fBEPERM\fR), \fBpriocntl()\fR continues to reset the
parameters for all target LWPs where the calling LWP has appropriate
permissions. The \fBpriocntl()\fR function returns \fB\(mi1\fR and \fBerrno\fR
is set to \fBEPERM\fR when the operation failed for one or more of the target
LWPs. All errors other than \fBEPERM\fR result in an immediate termination of
\fBpriocntl()\fR.
.RE

.SH REALTIME CLASS
The realtime class provides a fixed priority preemptive scheduling policy for
those LWPS requiring fast and deterministic response and absolute
user/application control of scheduling priorities. If the realtime class is
configured in the system, it should have exclusive control of the highest range
of scheduling priorities on the system. This ensures that a runnable realtime
LWP is given CPU service before any LWP belonging to any other class.
.sp
.LP
The realtime class has a range of realtime priority (\fIrt_pri\fR) values that
can be assigned to an LWP within the class. Realtime priorities range from 0 to
\fIx\fR, where the value of \fIx\fR is configurable and can be determined for a
specific installation by using the \fBpriocntl()\fR \fBPC_GETCID\fR or
\fBPC_GETCLINFO\fR command.
.sp
.LP
The realtime scheduling policy is a fixed priority policy. The scheduling
priority of a realtime LWP is never changed except as the result of an explicit
request by the user/application to change the \fIrt_pri\fR value of the LWP.
.sp
.LP
For an LWP in the realtime class, the \fIrt_pri\fR value is, for all practical
purposes, equivalent to the scheduling priority of the LWP. The \fIrt_pri\fR
value completely determines the scheduling priority of a realtime LWP relative
to other LWPs within its class. Numerically higher \fIrt_pri\fR values
represent higher priorities. Since the realtime class controls the highest
range of scheduling priorities in the system, it is guaranteed that the
runnable realtime LWP with the highest \fIrt_pri\fR value is always selected to
run before any other LWPs in the system.
.sp
.LP
In addition to providing control over priority, \fBpriocntl()\fR provides for
control over the length of the time quantum allotted to the LWP in the realtime
class. The time quantum value specifies the maximum amount of time an LWP can
run assuming that it does not complete or enter a resource or event wait state
(\fIsleep\fR). If another LWP becomes runnable at a higher priority, the
currently running LWP might be preempted before receiving its full time
quantum.
.sp
.LP
The realtime quantum signal can be used for the notification of runaway
realtime processes about the consumption of their time quantum. Those
processes, which are monitored by the realtime time quantum signal, receive the
configured signal in the event of time quantum expiration. The default value
(\fB0\fR) of the time quantum signal will denote no signal delivery and a
positive value will denote the delivery of the signal specified by the value.
The realtime quantum signal can be set with the \fBpriocntl()\fR
\fBPC_SETXPARMS\fR command and displayed with the \fBpriocntl()\fR
\fBPC_GETXPARMS\fR command as explained below.
.sp
.LP
The system's process scheduler keeps the runnable realtime LWPs on a set of
scheduling queues. There is a separate queue for each configured realtime
priority and all realtime LWPs with a given \fIrt_pri\fR value are kept
together on the appropriate queue. The LWPs on a given queue are ordered in
FIFO order (that is, the LWP at the front of the queue has been waiting longest
for service and receives the CPU first). Realtime LWPs that wake up after
sleeping, LWPs that change to the realtime class from some other class, LWPs
that have used their full time quantum, and runnable LWPs whose priority is
reset by \fBpriocntl()\fR are all placed at the back of the appropriate queue
for their priority. An LWP that is preempted by a higher priority LWP remains
at the front of the queue (with whatever time is remaining in its time quantum)
and runs before any other LWP at this priority. Following a \fBfork\fR(2)
function call by a realtime LWP, the parent LWP continues to run while the
child LWP (which inherits its parent's \fBrt_pri\fR value) is placed at the
back of the queue.
.sp
.LP
A \fBrtinfo_t\fR structure with the following members, defined in
\fB<sys/rtpriocntl.h>\fR, defines the format used for the attribute data for
the realtime class.
.sp
.in +2
.nf
short    rt_maxpri;      /* Maximum realtime priority */
.fi
.in -2

.sp
.LP
The \fBpriocntl()\fR \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands return
realtime class attributes in the \fIpc_clinfo\fR buffer in this format.
.sp
.LP
The \fBrt_maxpri\fR member specifies the configured maximum \fBrt_pri\fR value
for the realtime class. If \fIrt_maxpri\fR is \fBx\fR, the valid realtime
priorities range from 0 to \fIx\fR.
.sp
.LP
A \fBrtparms_t\fR structure with the following members, defined in
\fB<sys/rtpriocntl.h>\fR, defines the format used to specify the realtime
class-specific scheduling parameters of an LWP.
.sp
.in +2
.nf
short    rt_pri;       /* Real-Time priority */
uint_t   rt_tqsecs;    /* Seconds in time quantum */
int      rt_tqnsecs;   /* Additional nanoseconds in quantum */
.fi
.in -2

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETPARMS\fR or \fBPC_GETPARMS\fR
commands, if \fBpc_cid\fR specifies the realtime class, the data in the
\fIpc_clparms\fR buffer are in this format.
.sp
.LP
These commands can be used to set the realtime priority to the specified value
or get the current \fIrt_pri\fR value. Setting the \fBrt_pri\fR value of an LWP
that is currently running or runnable (not sleeping) causes the LWP to be
placed at the back of the scheduling queue for the specified priority. The LWP
is placed at the back of the appropriate queue regardless of whether the
priority being set is different from the previous \fIrt_pri\fR value of the
LWP. A running LWP can voluntarily release the CPU and go to the back of the
scheduling queue at the same priority by resetting its \fIrt_pri\fR value to
its current realtime priority value. To change the time quantum of an LWP
without setting the priority or affecting the LWP's position on the queue, the
\fIrt_pri\fR member should be set to the special value \fBRT_NOCHANGE\fR,
defined in \fB<sys/rtpriocntl.h>\fR. Specifying \fBRT_NOCHANGE\fR when changing
the class of an LWP to realtime from some other class results in the realtime
priority being set to 0.
.sp
.LP
For the \fBpriocntl()\fR \fBPC_GETPARMS\fR command, if \fIpc_cid\fR specifies
the realtime class and more than one realtime LWP is specified, the scheduling
parameters of the realtime LWP with the highest \fIrt_pri\fR value among the
specified LWPs are returned and the LWP ID of this LWP is returned by the
\fBpriocntl()\fR call. If there is more than one LWP sharing the highest
priority, the one returned is implementation-dependent.
.sp
.LP
The \fIrt_tqsecs\fR and \fIrt_tqnsecs\fR members are used for getting or
setting the time quantum associated with an LWP or group of LWPs.
\fIrt_tqsecs\fR is the number of seconds in the time quantum and
\fBrt_tqnsecs\fR is the number of additional nanoseconds in the quantum. For
example, setting \fIrt_tqsecs\fR to 2 and \fBrt_tqnsecs\fR to 500,000,000
(decimal) would result in a time quantum of two and one-half seconds.
Specifying a value of 1,000,000,000 or greater in the \fIrt_tqnsecs\fR member
results in an error return with \fBerrno\fR set to \fBEINVAL\fR. Although the
resolution of the \fItq_nsecs\fR member is very fine, the specified time
quantum length is rounded up by the system to the next integral multiple of the
system clock's resolution. The maximum time quantum that can be specified is
implementation-specific and equal to \fBINT_MAX\fR ticks. The \fBINT_MAX\fR
value is defined in \fB<limits.h>\fR. Requesting a quantum greater than this
maximum results in an error return with \fBerrno\fR set to \fBERANGE\fR,
although infinite quantums can be requested using a special value as explained
below. Requesting a time quantum of 0 by setting both \fIrt_tqsecs\fR and
\fBrt_tqnsecs\fR to 0 results in an error return with \fBerrno\fR set to
\fBEINVAL\fR.
.sp
.LP
The \fIrt_tqnsecs\fR member can also be set to one of the following special
values defined in \fB<sys/rtpriocntl.h>\fR, in which case the value of
\fIrt_tqsecs\fR is ignored:
.sp
.ne 2
.na
\fB\fBRT_TQINF\fR\fR
.ad
.RS 15n
Set an infinite time quantum.
.RE

.sp
.ne 2
.na
\fB\fBRT_TQDEF\fR\fR
.ad
.RS 15n
Set the time quantum to the default for this priority (see \fBrt_dptbl\fR(5)).
.RE

.sp
.ne 2
.na
\fB\fBRT_NOCHANGE\fR\fR
.ad
.RS 15n
Do not set the time quantum. This value is useful when you wish to change the
realtime priority of an LWP without affecting the time quantum. Specifying this
value when changing the class of an LWP to realtime from some other class is
equivalent to specifying \fBRT_TQDEF\fR.
.RE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETXPARMS\fR or \fBPC_GETXPARMS\fR
commands, the first argument after the command code must be the class name of
the realtime class (\fBRT\fR). The next arguments are formed as (key, value)
pairs, terminated by a \fB0\fR key. The definition for the keys of the realtime
class can be found in \fB<sys/rtpriocntl.h>\fR. A repeated specification of the
same key results in an error return and \fBerrno\fR set to \fBEINVAL\fR.
.sp

.sp
.TS
box;
c | c | c
l | l | l .
Key	Value Type	Description
_
\fBRT_KY_PRI\fR	\fBpri_t\fR	realtime priority
\fBRT_KY_TQSECS\fR	\fBuint_t\fR	seconds in time quantum
_
\fBRT_KY_TQNSECS\fR	\fBint\fR	nanoseconds in time quantum
_
\fBRT_KY_TQSIG\fR	\fBint\fR	realtime time quantum signal
.TE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_GETXPARMS\fR command, the value
associated with the key is always a pointer to a scheduling parameter of the
value type shown in the table above. In contrast, when using the
\fBpriocntl()\fR \fBPC_SETXPARMS\fR command, the scheduling parameter is given
as a direct value.
.sp
.LP
A \fBpriocntl()\fR \fBPC_SETXPARMS\fR command with the class name (\fBRT\fR)
and without a following (key, value) pair will set or reset all realtime
scheduling parameters of the target process(es) to their default values.
Changing the class of an LWP to realtime from some other class causes the
parameters to be set to their default values. The default realtime priority
(\fBRT_KY_PRI\fR) is \fB0\fR. A default time quantum (\fBRT_TQDEF\fR) is
assigned to each priority class (see \fBrt_dptbl\fR(5)). The default realtime
time quantum signal (\fBRT_KY_TQSIG\fR) is \fB0\fR.
.sp
.LP
The value associated with \fBRT_KY_TQSECS\fR is the number of seconds in the
time quantum. The value associated with \fBRT_KY_TQNSECS\fR is the number of
nanoseconds in the quantum. Specifying a value of 1,000,000,000 or greater for
the number of nanoseconds results in an error return and \fBerrno\fR is set to
\fBEINVAL\fR. The specified time quantum is rounded up by the system to the
next integral multiple of the system clock's resolution. The maximum time
quantum that can be specified is implementation-specific and equal to
\fBINT_MAX\fR ticks, defined in \fB<limits.h>\fR. Requesting a quantum greater
than this maximum results in an error return and \fBerrno\fR is set to
\fBERANGE\fR. If seconds (\fBRT_KY_TQSECS\fR) but no nanoseconds
(\fBRT_KY_TQNSECS\fR) are supplied, the number of nanoseconds is set to
\fB0\fR. If nanoseconds (\fBRT_KY_TQNSECS\fR) but no seconds
(\fBRT_KY_TQSECS\fR) are supplied, the number of seconds is set to \fB0\fR. A
time quantum of \fB0\fR (seconds and nanoseconds are \fB0\fR) results in an
error return with \fBerrno\fR set to \fBEINVAL\fR. Special values for
\fBRT_KY_TQSECS\fR are \fBRT_TQINF\fR and \fBRT_TQDEF\fR (as described above).
The \fBpriocntl()\fR command \fBPC_SETXPARMS\fR knows no special value
\fBRT_NOCHANGE\fR.
.sp
.LP
To change the class of an LWP to realtime from any other class, the LWP
invoking \fBpriocntl()\fR must have sufficient privileges. To change the
priority or time quantum setting of a realtime LWP, the LWP invoking
\fBpriocntl()\fR must have sufficient privileges or must itself be a realtime
LWP whose real or effective user ID matches the real of effective user ID of
the target LWP.
.sp
.LP
The realtime priority and time quantum are inherited across \fBfork\fR(2) and
the \fBexec\fR family of functions. When using the time quantum signal with a
user-defined signal handler across the \fBexec\fR functions, the new image must
install an appropriate user-defined signal handler before the time quantum
expires. Otherwise, unpredictable behavior might result.
.SH TIME-SHARING CLASS
The time-sharing scheduling policy provides for a fair and effective allocation
of the CPU resource among LWPs with varying CPU consumption characteristics.
The objectives of the time-sharing policy are to provide good response time to
interactive LWPs and good throughput to CPU-bound jobs, while providing a
degree of user/application control over scheduling.
.sp
.LP
The time-sharing class has a range of time-sharing user priority (see
\fIts_upri\fR below) values that can be assigned to LWPs within the class. A
\fIts_upri\fR value of 0 is defined as the default base priority for the
time-sharing class. User priorities range from \(mi\fIx\fR to +\fIx\fR where
the value of \fIx\fR is configurable and can be determined for a specific
installation by using the \fBpriocntl()\fR \fBPC_GETCID\fR or
\fBPC_GETCLINFO\fR command.
.sp
.LP
The purpose of the user priority is to provide some degree of user/application
control over the scheduling of LWPs in the time-sharing class. Raising or
lowering the \fIts_upri\fR value of an LWP in the time-sharing class raises or
lowers the scheduling priority of the LWP. It is not guaranteed, however, that
an LWP with a higher \fIts_upri\fR value will run before one with a lower
\fIts_upri\fR value, since the \fIts_upri\fR value is just one factor used to
determine the scheduling priority of a time-sharing LWP. The system can
dynamically adjust the internal scheduling priority of a time-sharing LWP based
on other factors such as recent CPU usage.
.sp
.LP
In addition to the system-wide limits on user priority (returned by the
\fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands) there is a per LWP user
priority limit (see \fIts_uprilim\fR below) specifying the maximum
\fIts_upri\fR value that can be set for a given LWP. By default,
\fIts_uprilim\fR is 0.
.sp
.LP
A \fBtsinfo_t\fR structure with the following members, defined in
\fB<sys/tspriocntl.h>\fR, defines the format used for the attribute data for
the time-sharing class.
.sp
.in +2
.nf
short    ts_maxupri;     /* Limits of user priority range */
.fi
.in -2

.sp
.LP
The \fBpriocntl()\fR \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands return
time-sharing class attributes in the \fBpc_clinfo\fR buffer in this format.
.sp
.LP
The \fBts_maxupri\fR member specifies the configured maximum user priority
value for the time-sharing class. If \fBts_maxupri\fR is \fIx\fR, the valid
range for both user priorities and user priority limits is from \(mi\fIx\fR to
+\fIx\fR.
.sp
.LP
A \fBtsparms_t\fR structure with the following members, defined in
\fB<sys/tspriocntl.h>\fR, defines the format used to specify the time-sharing
class-specific scheduling parameters of an LWP.
.sp
.in +2
.nf
short    ts_uprilim;     /* Time-Sharing user priority limit */
short    ts_upri;        /* Time-Sharing user priority */
.fi
.in -2

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETPARMS\fR or \fBPC_GETPARMS\fR
commands, if \fBpc_cid\fR specifies the time-sharing class, the data in the
\fBpc_clparms\fR buffer is in this format.
.sp
.LP
For the \fBpriocntl()\fR \fBPC_GETPARMS\fR command, if \fBpc_cid\fR specifies
the time-sharing class and more than one time-sharing LWP is specified, the
scheduling parameters of the time-sharing LWP with the highest \fIts_upri\fR
value among the specified LWPs is returned and the LWP ID of this LWP is
returned by the \fBpriocntl()\fR call. If there is more than one LWP sharing
the highest user priority, the one returned is implementation-dependent.
.sp
.LP
Any time-sharing LWP can lower its own \fIts_uprilim\fR (or that of another LWP
with the same user ID). Only a time-sharing LWP with sufficient privileges can
raise a \fIts_uprilim\fR. When changing the class of an LWP to time-sharing
from some other class, sufficient privileges are required to set the initial
\fIts_uprilim\fR to a value greater than 0. Attempts by an unprivileged LWP to
raise a \fIts_uprilim\fR or set an initial \fIts_uprilim\fR greater than 0 fail
with a return value of \(mi1 and \fBerrno\fR set to \fBEPERM\fR.
.sp
.LP
Any time-sharing LWP can set its own \fIts_upri\fR (or that of another LWP with
the same user ID) to any value less than or equal to the LWP's
\fIts_uprilim\fR. Attempts to set the \fIts_upri\fR above the \fIts_uprilim\fR
(and/or set the \fIts_uprilim\fR below the \fIts_upri\fR) result in the
\fIts_upri\fR being set equal to the \fIts_uprilim\fR.
.sp
.LP
Either of the \fIts_uprilim\fR or \fIts_upri\fR members can be set to the
special value \fBTS_NOCHANGE\fR, defined in \fB<sys/tspriocntl.h>\fR, to set
one of the values without affecting the other. Specifying \fBTS_NOCHANGE\fR for
the \fIts_upri\fR when the \fIts_uprilim\fR is being set to a value below the
current \fIts_upri\fR causes the \fIts_upri\fR to be set equal to the
\fIts_uprilim\fR being set. Specifying \fBTS_NOCHANGE\fR for a parameter when
changing the class of an LWP to time-sharing (from some other class) causes the
parameter to be set to a default value. The default value for the
\fIts_uprilim\fR is \fB0\fR and the default for the \fIts_upri\fR is to set it
equal to the \fIts_uprilim\fR that is being set.
.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETXPARMS\fR or \fBPC_GETXPARMS\fR
commands, the first argument after the command code is the class name of the
time-sharing class (\fBTS\fR). The next arguments are formed as (key, value)
pairs, terminated by a \fB0\fR key. The definition for the keys of the
time-sharing class can be found in \fB<sys/tspriocntl.h>\fR. A repeated
specification of the same key results in an error return and \fBerrno\fR set to
\fBEINVAL\fR.
.sp

.sp
.TS
box;
c | c | c
l | l | l .
Key	Value Type	Description
_
\fBTS_KY_UPRILIM\fR	\fBpri_t\fR	user priority limit
\fBTS_KY_UPRI\fR	\fBpri_t\fR	user priority
.TE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_GETXPARMS\fR command, the value
associated with the key is always a pointer to a scheduling parameter of the
value type in the table above. In contrast, when using the \fBpriocntl()\fR
\fBPC_SETXPARMS\fR command, the scheduling parameter is given as a direct
value.
.sp
.LP
A \fBpriocntl()\fR \fBPC_SETXPARMS\fR command with the class name (\fBTS\fR)
and without a following (key, value) pair will set or reset all time-sharing
scheduling parameters of the target process(es) to their default values.
Changing the class of an LWP to time-sharing from some other class causes the
parameters to be set to their default values. The default value for the user
priority limit (\fBTS_KY_UPRILIM\fR) is \fB0\fR. The default value for the user
priority (\fBTS_KY_UPRI\fR) is equal to the user priority limit
(\fBTS_KY_UPRILIM\fR) that is being set.
.sp
.LP
The \fBpriocntl()\fR command \fBPC_SETXPARMS\fR knows no special value
\fBTS_NOCHANGE\fR.
.sp
.LP
The time-sharing user priority and user priority limit are inherited across
\fBfork()\fR and the \fBexec\fR family of functions.
.SH INTERACTIVE CLASS
The interactive scheduling policy is a variation on the time-sharing scheduling
policy. All that can be said about the time-sharing scheduling policy is also
true for the interactive scheduling policy, with one addition: An LWP in the
interactive class with its \fIia_mode\fR value set to \fBIA_SET_INTERACTIVE\fR
has its time-sharing priority boosted by \fBIA_BOOST\fR (10).
.sp
.LP
An \fBiainfo_t\fR structure with the following members, defined in
\fB<sys/iapriocntl.h>\fR, defines the format used for the attribute data for
the interactive class.
.sp
.in +2
.nf
short    ia_maxupri;     /* Limits of user priority range */
.fi
.in -2

.sp
.LP
The \fBpriocntl()\fR \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands return
interactive class attributes in the \fIpc_clinfo\fR buffer in this format.
.sp
.LP
The \fIia_maxupri\fR member specifies the configured maximum user priority
value for the interactive class. If \fIia_maxupri\fR is \fBx\fR, the valid
range for both user priorities and user priority limits is from -x to +x.
.sp
.LP
A \fBiaparms_t\fR structure with the following members, defined in
\fB<sys/iapriocntl.h>\fR, defines the format used to specify the interactive
class-specific scheduling parameters of an LWP.
.sp
.in +2
.nf
short    ia_uprilim;     /* Interactive user priority limit */
short    ia_upri;        /* Interactive user priority */
int      ia_mode;        /* interactive on/off */
.fi
.in -2

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETPARMS\fR or \fBPC_GETPARMS\fR
commands, if \fIpc_cid\fR specifies the interactive class, the data in the
\fIpc_clparms\fR buffer is in this format.
.sp
.LP
For the \fBpriocntl()\fR \fBPC_GETPARMS\fR command, if \fIpc_cid\fR specifies
the interactive class and more than one interactive LWP is specified, the
scheduling parameters of the interactive LWP with the highest \fIia_upri\fR
value among the specified LWPs is returned and the LWP ID of this LWP is
returned by the \fBpriocntl()\fR call. If there is more than one LWP sharing
the highest user priority, the one returned is implementation-dependent.
.sp
.LP
All that is said above in the TIME-SHARING CLASS section concerning
manipulation of \fIts_uprilim\fR and \fIts_upri\fR applies equally to
manipulations of \fIia_uprilim\fR and \fIia_upri\fR in the interactive class.
.sp
.LP
When using the \fBPC_SETPARMS\fR command, the \fIia_mode\fR member must be set
to one of the values \fBIA_SET_INTERACTIVE\fR, \fBIA_INTERACTIVE_OFF\fR, or
\fBIA_NOCHANGE\fR, defined in \fB<sys/iapriocntl.h>\fR, to set the interactive
mode on or off or to make no change to the interactive mode.
.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETXPARMS\fR or \fBPC_GETXPARMS\fR
commands, the first argument after the command code is the class name of the
interactive class (IA). The next arguments are formed as (key, value) pairs,
terminated by a 0 key. The definition for the keys of the interactive class can
be found in \fB<sys/iapriocntl.h>\fR. A repeated specification of the same key
results in an error return and \fBerrno\fR set to \fBEINVAL\fR.
.sp

.sp
.TS
c c c
l l l .
Key	Value Type	Description
\fBIA_KY_UPRILIM\fR	\fBpri_t\fR	user priority limit
\fBIA_KY_UPRI\fR	\fBpri_t\fR	user priority
\fBIA_KY_MODE\fR	\fBint\fR	interactive mode
.TE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_GETXPARMS\fR command, the value
associated with the key is always a pointer to a scheduling parameter of the
value type in the table above. In contrast, when using the \fBpriocntl()\fR
\fBPC_SETXPARMS\fR command, the scheduling parameter is given as a direct
value.
.sp
.LP
A \fBpriocntl()\fR \fBPC_SETXPARMS\fR command with the class name (IA) and
without a following (key, value) pair will set or reset all interactive
scheduling parameters of the target process(es) to their default values.
Changing the class of an LWP to interactive from some other class causes the
parameters to be set to their default values. The default value for the user
priority limit (\fBIA_KY_UPRILIM\fR) is 0. The default value for the user
priority (\fBIA_KY_UPRI\fR) is equal to the user priority limit
(\fBIA_KY_UPRILIM\fR) that is being set. The default value for the interactive
mode (\fBIA_KY_MODE\fR) is \fBIA_SET_INTERACTIVE\fR.
.sp
.LP
The \fBpriocntl()\fR command \fBPC_SETXPARMS\fR knows no special value
\fBIA_NOCHANGE\fR.
.sp
.LP
The interactive user priority and user priority limit are inherited across fork
and the exec family of functions.
.SH FAIR-SHARE CLASS
The fair-share scheduling policy provides a fair allocation of CPU resources
among projects, independent of the number of processes they contain. Projects
are given "shares" to control their quota of CPU resources. See \fBFSS\fR(4)
for more information about how to configure shares.
.sp
.LP
The fair share class supports the notion of per-LWP user priority (see
\fBfss_upri\fR below) values for compatibility with the time-sharing scheduling
class. An \fIfss_upri\fR value of 0 is defined as the default base priority for
the fair-share class. User priorities range from -\fIx\fR to +\fIx\fR where the
value of \fIx\fR is configurable and can be determined for a specific
installation by using the \fBpriocntl()\fR \fBPC_GETCID\fR or
\fBPC_GETCLINFO\fR command.
.sp
.LP
The purpose of the user priority is to provide some degree of user/application
control over the scheduling of LWPs in the fair-share class. Raising the
\fBfss_upri\fR value of an LWP in the fair-share class tells the scheduler to
give this LWP more CPU time slices, while lowering the \fBfss_upri\fR value
tells the scheduler to give it less CPU slices. It is not guaranteed, however,
that an LWP with a higher \fBfss_upri\fR value will run before one with a lower
\fBfss_upri\fR value. This is because the \fBfss_upri\fR value is just one
factor used to determine the scheduling priority of a fair-share LWP. The
system can dynamically adjust the internal scheduling priority of a fair-share
LWP based on other factors such as recent CPU usage. The fair-share scheduler
attempts to provide an evenly graded effect across the whole range of user
priority values.
.sp
.LP
User priority values do not interfere with project shares. That is, changing a
user priority value of a process does not have any effect on its project CPU
entitlement, which is based on the number of shares it is allocated in
comparison with other projects.
.sp
.LP
In addition to the system-wide limits on user priority (returned by the
\fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands), there is a per-LWP user
priority limit (see \fIfss_uprilim\fR below) that specifies the maximum
\fBfss_upri\fR value that can be set for a given LWP. By default,
\fIfss_uprilim\fR is 0.
.sp
.LP
A \fBfssinfo_t\fR structure with the following members, defined in
\fB<sys/fsspriocntl.h>\fR, defines the format used for the attribute data for
the fair-share class.
.sp
.in +2
.nf
short    fss_maxupri;    /* Limits of user priority range */
.fi
.in -2

.sp
.LP
The \fBpriocntl()\fR \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands return
fair-share class attributes in the \fIpc_clinfo\fR buffer in this format.
.sp
.LP
\fIfss_maxupri\fR specifies the configured maximum user priority value for the
fair-share class. If \fBfss_maxupri\fR is \fIx\fR, the valid range for both
user priorities and user priority limits is from -\fIx\fR to +\fIx\fR.
.sp
.LP
A \fBfssparms_t\fR structure with the following members, defined in
\fB<sys/fsspriocntl.h>\fR, defines the format used to specify the fair-share
class-specific scheduling parameters of an LWP.
.sp
.in +2
.nf
short    fss_uprilim;   /* Fair-share user priority limit */
short    fss_upri;      /* Fair-share user priority */
.fi
.in -2

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETPARMS\fR or \fBPC_GETPARMS\fR
commands, if \fIpc_cid\fR specifies the fair-share class, the data in the
\fIpc_clparms\fR buffer is in this format.
.sp
.LP
For the \fBpriocntl()\fR \fBPC_GETPARMS\fR command, if \fIpc_cid\fR specifies
the fair-share class and more than one fair-share LWP is specified, the
scheduling parameters of the fair-share LWP with the highest \fIfss_upri\fR
value among the specified LWPs is returned and the LWP ID of this LWP is
returned by the \fBpriocntl()\fR call. If there is more than one LWP sharing
the highest user priority, the one returned is implementation-dependent.
.sp
.LP
Any fair-share LWP can lower its own \fIfss_uprilim\fR (or that of another LWP
with the same user ID). Only a fair-share LWP with sufficient privileges can
raise an \fIfss_uprilim\fR. When changing the class of an LWP to fair-share
from some other class, sufficient privileges are required to enter the FSS
class or to set the initial \fIfss_uprilim\fR to a value greater than 0.
Attempts by an unprivileged LWP to raise an \fIfss_uprilim\fR or set an initial
\fIfss_uprilim\fR greater than 0 fail with a return value of -1 and \fBerrno\fR
set to \fBEPERM\fR.
.sp
.LP
Any fair-share LWP can set its own \fIfss_upri\fR (or that of another LWP with
the same user ID) to any value less than or equal to the LWP's
\fIfss_uprilim\fR. Attempts to set the \fBfss_upri\fR above the
\fBfss_uprilim\fR (and/or set the \fIfss_uprilim\fR below the \fIfss_upri\fR)
result in the \fIfss_upri\fR being set equal to the \fIfss_uprilim\fR.
.sp
.LP
Either of the \fIfss_uprilim\fR or \fBfss_upri\fR members can be set to the
special value \fBFSS_NOCHANGE\fR (defined in \fB<sys/fsspriocntl.h>\fR) to set
one of the values without affecting the other. Specifying \fBFSS_NOCHANGE\fR
for the \fIfss_upri\fR when the \fIfss_uprilim\fR is being set to a value below
the current \fIfss_upri\fR causes the \fIfss_upri\fR to be set equal to the
\fIfss_uprilim\fR being set. Specifying \fBFSS_NOCHANGE\fR for a parameter when
changing the class of an LWP to fair-share (from some other class) causes the
parameter to be set to a default value. The default value for the
\fBfss_uprilim\fR is 0 and the default for the \fBfss_upri\fR is to set it
equal to the \fIfss_uprilim\fR which is being set.
.sp
.LP
The fair-share user priority and user priority limit are inherited across
\fBfork()\fR and the \fBexec\fR family of functions.
.SH FIXED-PRIORITY CLASS
The fixed-priority class provides a fixed-priority preemptive scheduling policy
for those LWPs requiring that the scheduling priorities do not get dynamically
adjusted by the system and that the user/application have control of the
scheduling priorities.
.sp
.LP
The fixed-priority class has a range of fixed-priority user priority (see
\fBfx_upri\fR below) values that can be assigned to LWPs within the class. A
\fIfx_upri\fR value of 0 is defined as the default base priority for the
fixed-priority class. User priorities range from 0 to \fIx\fR where the value
of \fIx\fR is configurable and can be determined for a specific installation by
using the \fBpriocntl()\fR \fBPC_GETCID\fR or \fBPC_GETCLINFO\fR command.
.sp
.LP
The purpose of the user priority is to provide user/application control over
the scheduling of processes in the fixed-priority class. For processes in the
fixed-priority class, the \fIfx_upri\fR value is, for all practical purposes,
equivalent to the scheduling priority of the process. The \fIfx_upri\fR value
completely determines the scheduling priority of a fixed-priority process
relative to other processes within its class. Numerically higher \fIfx_upri\fR
values represent higher priorities.
.sp
.LP
In addition to the system-wide limits on user priority (returned by the
\fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands), there is a per-LWP user
priority limit (see \fIfx_uprilim\fR below) that specifies the maximum
\fIfx_upri\fR value that can be set for a given LWP. By default,
\fIfx_uprilim\fR is 0.
.sp
.LP
A structure with the following member (defined in \fB<sys/fxpriocntl.h>\fR)
defines the format used for the attribute data for the fixed-priority class.
.sp
.in +2
.nf
pri_t   fx_maxupri;      /* Maximum user priority */
.fi
.in -2

.sp
.LP
The \fBpriocntl()\fR \fBPC_GETCID\fR and \fBPC_GETCLINFO\fR commands return
fixed-priority class attributes in the \fIpc_clinfo\fR buffer in this format.
.sp
.LP
The \fIfx_maxupri\fR member specifies the configured maximum user priority
value for the fixed-priority class. If \fIfx_maxupri\fR is \fIx\fR, the valid
range for both user priorities and user priority limits is from 0 to \fIx\fR.
.sp
.LP
A structure with the following members (defined in \fB<sys/fxpriocntl.h>\fR)
defines the format used to specify the fixed-priority class-specific scheduling
parameters of an LWP.
.sp
.in +2
.nf
pri_t    fx_upri;     /* Fixed-priority user priority */
pri_t    fx_uprilim;  /* Fixed-priority user priority limit */
uint_t   fx_tqsecs;   /* seconds in time quantum */
int      fx_tqnsecs;  /* additional nanosecs in time quant */
.fi
.in -2

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETPARMS\fR or \fBPC_GETPARMS\fR
commands, if \fIpc_cid\fR specifies the fixed-priority class, the data in the
\fIpc_clparms\fR buffer is in this format.
.sp
.LP
For the \fBpriocntl()\fR \fBPC_GETPARMS\fR command, if \fIpc_cid\fR specifies
the fixed-priority class and more than one fixed-priority LWP is specified, the
scheduling parameters of the fixed-priority LWP with the highest \fIfx_upri\fR
value among the specified LWPs is returned and the LWP ID of this LWP is
returned by the \fBpriocntl()\fR call. If there is more than one LWP sharing
the highest user priority, the one returned is implementation-dependent.
.sp
.LP
Any fixed-priority LWP can lower its own \fIfx_uprilim\fR (or that of another
LWP with the same user ID). Only a fixed-priority LWP with sufficient
privileges can raise a \fIfx_uprilim\fR. When changing the class of an LWP to
fixed-priority from some other class, sufficient privileges are required to set
the initial \fIfx_uprilim\fR to a value greater than 0. Attempts by an
unprivileged LWP to raise a \fIfx_uprilim\fR or set an initial \fBfx_uprilim\fR
greater than 0 fail with a return value of -1 and errno set to \fBEPERM\fR.
.sp
.LP
Any fixed-priority LWP can set its own \fIfx_upri\fR (or that of another LWP
with the same user ID) to any value less than or equal to the LWP's
\fIfx_uprilim\fR. Attempts to set the \fIfx_upri\fR above the \fBfx_uprilim\fR
(and/or set the \fIfx_uprilim\fR below the \fIfx_upri\fR) result in the
\fBfx_upri\fR being set equal to the \fIfx_uprilim\fR.
.sp
.LP
Either of the \fIfx_uprilim\fR or \fIfx_upri\fR members can be set to the
special value \fBFX_NOCHANGE\fR (defined in \fB<sys/fxpriocntl.h>\fR) to set
one of the values without affecting the other. Specifying \fBFX_NOCHANGE\fR for
the \fIfx_upri\fR when the \fIfx_uprilim\fR is being set to a value below the
current \fIfx_upri\fR causes the \fIfx_upri\fR to be set equal to the
\fIfx_uprilim\fR being set. Specifying \fBFX_NOCHANGE\fR for a parameter when
changing the class of an LWP to fixed-priority (from some other class) causes
the parameter to be set to a default value. The default value for the
\fIfx_uprilim\fR is 0 and the default for the \fIfx_upri\fR is to set it equal
to the \fIfx_uprilim\fR that is being set. The default for time quantum is
dependent on the \fIfx_upri\fR and on the system configuration; see
\fBfx_dptbl\fR(5).
.sp
.LP
The \fIfx_tqsecs\fR and \fIfx_tqnsecs\fR members are used for getting or
setting the time quantum associated with an LWP or group of LWPs.
\fIfx_tqsecs\fR is the number of seconds in the time quantum and
\fIfx_tqnsecs\fR is the number of additional nanoseconds in the quantum. For
example, setting \fIfx_tqsecs\fR to 2 and \fIfx_tqnsecs\fR to 500,000,000
(decimal) would result in a time quantum of two and one-half seconds.
Specifying a value of 1,000,000,000 or greater in the \fIfx_tqnsecs\fR member
results in an error return with \fBerrno\fR set to \fBEINVAL\fR. Although the
resolution of the \fItq_nsecs\fR member is very fine, the specified time
quantum length is rounded up by the system to the next integral multiple of the
system clock's resolution. The maximum time quantum that can be specified is
implementation-specific and equal to \fBINT_MAX\fR ticks (defined in
\fB<limits.h>\fR). Requesting a quantum greater than this maximum results in an
error return with \fBerrno\fR set to \fBERANGE\fR, although infinite quantums
can be requested using a special value as explained below. Requesting a time
quantum of 0 (setting both \fIfx_tqsecs\fR and \fIfx_tqnsecs\fR to 0) results
in an error return with \fBerrno\fR set to \fBEINVAL\fR.
.sp
.LP
The \fIfx_tqnsecs\fR member can also be set to one of the following special
values (defined in \fB<sys/fxpriocntl.h>\fR), in which case the value of
\fIfx_tqsecs\fR is ignored:
.sp
.ne 2
.na
\fB\fBFX_TQINF\fR\fR
.ad
.RS 15n
Set an infinite time quantum.
.RE

.sp
.ne 2
.na
\fB\fBFX_TQDEF\fR\fR
.ad
.RS 15n
Set the time quantum to the default for this priority (see \fBfx_dptbl\fR(5)).
.RE

.sp
.ne 2
.na
\fB\fBFX_NOCHANGE\fR\fR
.ad
.RS 15n
Do not set the time quantum. This value is useful in changing the user priority
of an LWP without affecting the time quantum. Specifying this value when
changing the class of an LWP to fixed-priority from some other class is
equivalent to specifying \fBFX_TQDEF\fR.
.RE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_SETXPARMS\fR or \fBPC_GETXPARMS\fR
commands, the first argument after the command code must be the class name of
the fixed-priority class (FX). The next arguments are formed as (key, value)
pairs, terminated by a 0 key. The definition for the keys of the fixed-priority
class can be found in \fB<sys/fxpriocntl.h>\fR. A repeated specification of the
same key results in an error return and \fBerrno\fR set to \fBEINVAL\fR.
.sp

.sp
.TS
box;
c | c | c
l | l | l .
Key	Value Type	Description
_
\fBFX_KY_UPRILIM\fR	\fBpri_t\fR	user priority limit
\fBFX_KY_UPRI\fR	\fBpri_t\fR	user priority
_
\fBFX_KY_TQSECS\fR	\fBuint_t\fR	seconds in time quantum
_
\fBFX_KY_TQNSECS\fR	\fBint\fR	nanoseconds in time quantum
.TE

.sp
.LP
When using the \fBpriocntl()\fR \fBPC_GETXPARMS\fR command, the value
associated with the key is always a pointer to a scheduling parameter of the
value type shown in the table above. In contrast, when using the
\fBpriocntl()\fR \fBPC_SETXPARMS\fR command, the scheduling parameter is given
as a direct value.
.sp
.LP
A \fBpriocntl()\fR \fBPC_SETXPARMS\fR command with the class name (FX) and
without a following (key, value) pair will set or reset all realtime scheduling
parameters of the target process(es) to their default values. Changing the
class of an LWP to fixed-priority from some other class causes the parameters
to be set to their default values. The default value for the user priority
limit (\fBFX_KY_UPRILIM\fR) is 0. The default value for the user priority
(\fBFX_KY_UPRI\fR) is equal to the user priority limit (\fBFX_KY_UPRILIM\fR)
that is being set. A default time quantum (\fBFX_TQDEF\fR) is assigned to each
priority class (see \fBfx_dptbl\fR(5)).
.sp
.LP
The value associated with \fBFX_KY_TQSECS\fR is the number of seconds in the
time quantum. The value associated with \fBFX_KY_TQNSECS\fR is the number of
nanoseconds in the quantum. Specifying a value of 1,000,000,000 or greater for
the number of nanoseconds results in an error return and \fBerrno\fR is set to
\fBEINVAL\fR. The specified time quantum is rounded up by the system to the
next integral multiple of the system clock's resolution. The maximum time
quantum that can be specified is implementation-specific and equal to
\fBINT_MAX\fR ticks, defined in \fB<limits.h>\fR. Requesting a quantum greater
than this maximum results in an error return and \fBerrno\fR is set to
\fBERANGE\fR. If seconds (\fBFX_KY_TQSECS\fR) but no nanoseconds
(\fBFX_KY_TQNSECS\fR) are supplied, the number of nanoseconds is set to 0. If
nanoseconds (\fBFX_KY_TQNSECS\fR) but no seconds (\fBFX_KY_TQSECS\fR) are
supplied, the number of seconds is set to 0. A time quantum of 0 (seconds and
nanoseconds are 0) results in an error return with \fBerrno\fR set to
\fBEINVAL\fR. Special values for \fBFX_KY_TQSECS\fR are \fBFX_TQINF\fR and
\fBFX_TQDEF\fR (as described above). The \fBpriocntl()\fR command
\fBPC_SETXPARMS\fR knows no special value \fBFX_NOCHANGE\fR.
.sp
.LP
The fixed-priority user priority and user priority limit are inherited across
\fBfork\fR(2) and the \fBexec\fR family of functions.
.SH RETURN VALUES
Unless otherwise noted above, \fBpriocntl()\fR returns \fB0\fR on success. On
failure, \fBpriocntl()\fR returns \fB\(mi1\fR and sets \fBerrno\fR to indicate
the error.
.SH ERRORS
The \fBpriocntl()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 10n
An attempt to change the class of an LWP failed because of insufficient
resources other than memory (for example, class-specific kernel data
structures).
.RE

.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 10n
One of the arguments points to an illegal address.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The argument \fIcmd\fR was invalid, an invalid or unconfigured class was
specified, or one of the parameters specified was invalid.
.RE

.sp
.ne 2
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 10n
An attempt to change the class of an LWP failed because of insufficient memory.
.RE

.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 10n
The {\fBPRIV_PROC_PRIOCNTL\fR} privilege is not asserted in the effective set
of the calling LWP.
.sp
The calling LWP does not have sufficient privileges to affect the target LWP.
.RE

.sp
.ne 2
.na
\fB\fBERANGE\fR\fR
.ad
.RS 10n
The requested time quantum is out of range.
.RE

.sp
.ne 2
.na
\fB\fBESRCH\fR\fR
.ad
.RS 10n
None of the specified LWPs exist.
.RE

.SH SEE ALSO
.BR priocntl (1),
.BR exec (2),
.BR fork (2),
.BR nice (2),
.BR priocntlset (2),
.BR fx_dptbl (5),
.BR process (5),
.BR rt_dptbl (5),
.BR privileges (7),
.BR dispadmin (8),
.BR init (8)
.sp
.LP
\fISystem Administration Guide: Basic Administration\fR
.sp
.LP
\fIProgramming Interfaces Guide\fR
